1. Technical Field of the Invention
The invention concerns a solenoid-actuated latchable relay that operates in response to Alternating Current (AC). More particularly, the invention concerns such a relay that is controlled by a microprocessor to operate electrical devices such as motors and refrigeration equipment.
2. Description of Related Art
It has long been known that switching relays may be operated with solenoids. A solenoid is an electromagnet that has an energized coil approximately cylindrical in form, with an armature or plunger that moves in response to energization of the coil. Typically, the armature or plunger reciprocates along its axis within and along the axis of the coil when the coil is energized by a Direct Current (DC) signal. It is known that the armature or plunger may open and close relay contacts in response to energization of the coil.
Direct current energization has typically been used to operate solenoids. Thus, for example, a DC signal of a particular polarity is typically applied to continuously energize the coil of the solenoid and hold the plunger or armature in a desired operational position. One disadvantage of this operation is that power is continuously dissipated in order to continuously energize the coil and thereby maintain the solenoid in a desired operational position. Another disadvantage of such solenoids is that they are not amenable to operation in an AC electrical environment unless the energization signal for the solenoid is rectified. Also, for many uses of solenoids, a change in the polarity of the signal applied to the coil does not define a different operational condition.
Accordingly, it would be desirable to have a solenoid-actuated relay that operates with an AC energization signal, for example, the standard 60-hertz power signal that is used in the United States or the 50 hertz power signal used abroad. It would also be desirable to provide such a relay with different operational conditions in response to a change in polarity of the energizing AC signal. Further advantages could be achieved by surface mounting the relay to printed circuit boards and making the relay latchable so that it maintains its operational state without requiring the application of continuous power. Such relays would be particularly desirable for use in controlling AC electrical devices, for example, motors, compressors, evaporators and even heaters for various uses, including refrigeration equipment.
The invention concerns a solenoid-actuated latchable relay that may be used to control any mechanical or electrical devices, including motors, compressors, evaporators and heaters, particularly for use in refrigeration. The invention concerns controlling the operation of a solenoid relay by use of a triac that applies AC energization signals of selected polarity to a coil of the relay. As an example, one polarity would define one associated operational state of the solenoid-actuated relay such as closing switch contracts, and the reverse polarity would define an opposite operational state, such as opening the switch contracts.
The triac is controlled by a microprocessor that selects positive or negative portions of the AC power signal as required to energize the coil of the solenoid. Thus, for example, a portion of the positive cycle of the AC signal energizes the solenoid with a single positive polarity pulse and closes relay contacts to turn on an electrical apparatus. A latching mechanism holds the contacts in the closed position without continuously energizing the solenoid. The negative cycle of the AC input signal is selected by the microprocessor to energize the solenoid with a negative polarity pulse and thereby open the switch contacts which are then held open by the latching mechanism.
The switchable latching relay of the invention can be surface mounted on printed circuit boards and used to control the operation of any desired mechanical or electrical equipment, including motors, compressors, evaporators and heaters such as are employed to operate refrigerators. These and other benefits and features of the latchable relay of the invention will become apparent upon consideration of the following detailed description and accompanying drawings of presently preferred embodiments.